To keep the touch feeling of a yarn from deteriorating and prevent yarn breakage from occurring when carrying out fluff binding of the yarn, especially wool yarn.

High-temperature compressed air is fed to a nozzle 20 to reserve heat in an element (b). A pressurized gas at normal temperature is then fed to the nozzle 20 and jetted from jetting holes (i) and (j) in the tangential direction toward the inner peripheral surface of a yarn guide hole (d) to turn the yarn Y at a high speed and carry out the fluff binding treatment. The swirling gas stream kept at a high temperature and a low humidity by applying the heat from the element (b) to the compressed air does not deteriorate the unique soft touch feeling of the yarn Y because short fluffs are left. Since the swirling gas stream is heated with the heat accumulated in the element (b), an excessive temperature rise of the swirling gas stream is prevented to prevent the yarn breakage. The yarn Y is turned while being brought into contact with the inner surface S of a yarn feed guide passage, and the yarn Y is directly heated by heat conduction. Thereby, the rigidity is lowered to facilitate the binding of the fluffs. In this state, the surface of the yarn Y is passed over the inner surface S of the yarn feed guide passage. As a result, the fluffs are effectively bound.